Two-Phonon Spectrum of Diamond

Abstract

A careful calculation of the one-phonon dispersion in diamond reveals a shallow maximum in the [100] direction for the ${{\Delta }_2}^{\prime }\left(\mathrm{L}\mathrm{O}\right)$ branch. The two-phonon (overtone) density of states shows a sharp peak near twice the Raman frequency. This supports the interpretation of an observed peak in two-phonon Raman scattering as a simple overtone without the need to invoke a two-phonon bound state.